Ignitor for automatically starting arc lamps

ABSTRACT

A solid elongated refractory ignitor, having a pointed projection on one end and a bifurcated slot at the opposite end, is positioned between, and in contact with, electrode rods of an arc lamp to improve arc striking therebetween. The ejectable ignitor provides an initial short circuit between the electrodes so that during application of a power supply between the electrodes, an arc will be automatically struck therebetween without the need for manual manipulation of either or both electrodes by an operator.

United States Patent Hunsaker et al.

[54] IGNITOR FOR AUTOMATICALLY STARTING ARC LAMPS [72] lnventors: Floyd Melvin Hunsalter, Amherst, N.l-l.; Allan Joseph Quiring, Middleburg Heights, Ohio 7 [73] Assignee: Union Carbide Corporation, New York,

[22] Filed: Sept. 30, 1970 [21] Appl.No.: 76,677

[52] U.S.Cl ..313/l98,3l3/2l7,3l3/2l8, 314/34 [51] lnt.Cl. ..ll05b31/30 [58] Field ofSearch ..3l3/l84, 197, 198,217, 218;- 314/34 [56] References Cited UNITED STATES PATENTS 3,256,459 6/1966 Keller et al ..313/184X 7/1970 Scharf .314/34 [4 1 Feb. 22, 1972 Primary ExaminerRaymond F. Hossfeld Attorney-Paul A. Rose, Harrie M. Humphreys, Robert C. Cummings and Cornelius F. O'Brien [57} ABSTRACT A solid elongated refractory ignitor, having a pointed projection on one end and a bifurcated slot at the opposite end, is positioned between, and in contact with, electrode rods of an arc lamp to improve are striking therebetween. The ejectable ignitor provides an initial short circuit between the electrodes so that during application of a power supply between the electrodes, an arc will be automatically struck therebetween without the need for manual manipulation of either or both electrodes by an operator.

'7 V, w i s ..wa w re PATENTEDFEB22 I972 3,544, 774

FIG 20. FIG 2b. F/GI 2c.

F/G. 2a. F/G 28. FIG 2!? 46 INVENTO Floyd M. Hun er BY Allan U. Quiring ATTORNLEY IGNITOR FOR AUTOMATICALLY STARTING ARC LAMPS FIELD OF THE INVENTION This invention relates to are lamps and specifically to a means for improving initial and subsequent are striking between electrode rods in carbon arc lamps.

DESCRIPTION OF THE PRIOR ART Carbon arc lamps produce a high-intensity light source which makes them suitable for such applications as search lights, motion picture projector lamps, solar simulation apparatus and the like. The essential elements of an arc lamp comprises two electrode rods spaced apart by a predetermined gap dimension and a conventional power supply. The positive terminal of the power supply is coupled to the end of one electrode rod while the negative terminal is coupled to the end of the second electrode rod. This provides a series connection between the elements with the gap serving as an opening or break in the circuit. With the power supply connected to the electrode rods, the dimension of the gap is decreased until an arc is struck across the gap between the positively polarized rod and the negatively polarized rod. The gap is then increased until an optimum length is obtained which will produce a high-intensity light source in the crater region of the positively polarized rod. This high-intensity light is then appropriately focused to provide a source of illumination for various applications as specified above.

The striking of an arc lamp generally requires the application of a high voltage pulse to break down the dielectric medium, usually air, existing in and around the gap between the electrode rods. To eliminate the necessity of initial high-voltage pulsing, it has been common practice for an operator to manually adjust the length of the gap to such a dimension that an arc can be struck by application ofa regular operating voltage potential and then to increase the gap length by manually adjusting at least one of the electrode rods until the optimum gap dimension is obtained. Obviously, this latter procedure has to be carried out with care to avoid separating the gap to a point where the arc will be extinguished.

To overcome the problems associated with the manual manipulation ofthe electrode rods to initiate the striking of an arc, and to circumvent the need for initial high-voltage pulsing. several mechanisms have been designed with selfstarting features for automatic arc striking. For example, US. Pat. No. 3,256,459 discloses an arc lamp in which a conductive fusion bridge spans the gap between electrode rods and forms a low resistance electrical path therebetween. The fusion bridge is shaped such that its cross-sectional area progressively increases axially in the direction of one or both electrodes. A starting voltage vaporized the bridge from the minimum cross section area outward toward the electrodes thereby creating a progressively larger gap. Such a construction, however, is costly, has a poor shock resistance and requires expensive support and alignment equipment.

U.S. Pat. No. 3,377,497 describes another self-starting arc lamp wherein a conductive wire of substantially uniform cross section is used to bridge the gap between electrode rods. The wire is secured to the tapered end of each electrode rod by spot-welding means and at least one slot is cut into the peripheral surface of each tapered end portion of the electrode rod so that the bridge-wire can be axially suspended between and firmly secured along the arc end of the electrode rods. The wire is of a diameter sufficiently small to permit it to fuse or burn out before the arc lamp is damaged by the initial current flow. While this construction is somewhat successful, it also has several disadvantages. Much time and labor is expended in attempting to affix the wire to the electrode rods since both welding and machining operations are required for proper implementation of this device.

US. Pat. No. 3,52 1,! 14 describes another approach for the self-starting of arc lamps. An annular refractory tube designed for automatic are striking is positioned between and in contact with electrode rods of an arc lamp. The application of a supply potential causes the initial current to flow through the tube thereby striking an arc across the gap between the electrode rods. Immediately upon arcing, the tube is automatically ejected leaving the arc lamp in the operating mode. This automatic are starting device provides a good means for striking an are between new electrode rods without the need for manually maneuvering the electrode rods to obtain the optimum gap length.

Other self-starting arc lamp devices have been developed but all are either too complex, too costly and/or require excessive labor effort to secure or assemble the self-starting component to the electrode rods.

It is the object of this invention to provide a self-starting arc lamp employing an ignitor to facilitate automatic striking of an are between new or partially consumed electrode rods.

SUMMARY OF THE INVENTION This invention relates to a.solid elongated refractory ignitor designed to be positioned between, and in contact with, the electrode rods of a carbon arc lamp. The ignitor is designed with a pointed projection on one end and a bifurcated or twoprong configuration at the opposite end. The bifurcated end of the ignitor is so shaped so that it can partially sandwich a lip projection on the end of a positively polarized electrode rod while the pointed projected end of the ignitor can contact and securely rest upon, or be inserted into, the end of a negatively polarized electrode rod. In some instances, the pointed projected end of the ignitor can also be fabricated with a small bifurcated configuration that can slightly penetrate the electrode rod tip to secure contact therewith or slide upon and partially sandwich an appropriately shaped lip projection at the end of the negative electrode rod. In either case the ignitor should be properly secured between the electrode rods.

The bifurcated configuration can be composed of two or more linear surfaces which together provide a two-prong contour which can slide upon and engage a peripheral lip projection at the end of an electrode rod. The conventional V and U" shapes are only examples of the many contours possessing a two-prong form.

The pointed projectional configuration of the ignitor is intended to include any projection whereby the diameter or cross-sectional area at the tip of the projection is smaller than the average diameter or cross-sectional area, respectively, of the elongated body of the ignitor. For example, this includes conical, triangular, polygonial and any other similar shaped projections.

The unique feature of the ignitor is that it permits the optimum gap length between the electrode rods to be maintained during initial are striking of new or partially consumed electrode rods. The greater depth of the crater region of a partially consumed electrode rod does not effect the assembling procedure necessary to secure the ignitor between the electrode rods while maintaining the optimum gap length constant. Contrary to this, the hollow tube device of the prior art can not be assembled between partially consumed electrode rods while maintaining the optimum gap length therebetween.

The ignitor is easily secured to the electrode rods and is then automatically ejected from the gap upon the striking of the arc thereby eliminating the necessity of manually maneuvering either or both electrode rods by the operator to obtain optimum gap length.

In carbon arc lamps, the negatively polarizedelectrode rod 4 is usually fabricated with a conical or tapered shape at one end while the positively polarized electrode rod is machined with a recess at one of its ends, such recess providing a crater for the arc during the operational mode of the lamp from which a high intensity light source is localized. These ends of the electrode rods are spaced apart and form the gap where the arcing occurs. In addition to the recess in the positive electrode rod, a peripheral lip projection usually surrounds the crater. It is this positive lip projection that is engaged in the bifurcated contour of the ignitor. The pointed projected end of the ignitor is then projected upon, and secured to, the tapered end of the negative electrode rod. The contact area between the bifurcated contour of the ignitor and the lip projection on the positive rod is variable so that the optimum gap length can be maintained constant at all times since the electrode rods will not have to be moved to accommodate the securement of the ignitor to the rods even after the rods have been partially consumed.

Once the optimum gap length is obtained, the ignitor is easily positioned in place forming an electrical connection between the rods. The power is then applied to the electrode rods, by any suitable conventional means, and immediately the ignitor acts as a short thereby providing an ionization path between the electrode rods which facilitates the striking of an arc therebetween. With the ignitionof the arc, the ignitor is immediately dislodged from its position and falls free. The positive ejection of the ignitor from the gap position is believed to be due to the oxidation or burning of the ignitor, 2

and/or to the electrical force exerted due to the breakdown of the dielectric medium at the vicinity of the gap and/or to the rotation of the positive electrode rod.

When the illumination from the arc lamp is no longer required, the power is disconnected and the arc terminates. The same or another ignitor is then easily assembled in place between the electrode rods and the arc lamp is once again set for automatic starting.

The ignitor can be composed of any refractory material which can provide good electrical conductivity and thermal resistance. Such materials can be selected from at least one of the group consisting of carbon 'which is intended to include graphite, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum and tungsten. Any one of these materials can withstand the extreme temperatures existing in the arc region during are striking and therefore can be reused after they are ejected from the gap region upon arcing.

Carbonaceous materials ranging from lampblack base to coke base have been successfully tested and found to be commercially usable. In addition, at least one arc supporter commonly employed in the negative carbon rod and known to the trade, can be added in various concentrations in the carbonaceous material to form a composite suitable for use as an ignitor. Such arc supporters include the sulfur and silicon compounds of such elements as cesium, rubidium, potassium, calcium and the like.

The invention will become more apparent from the following description and claims taken in conjunction with the drawings wherein:

FIG. 10 is a perspective view of part of an angular trim arrangement of an arc lamp employing a refractory ignitor for self-starting.

FIG. lb is a perspective view of part ofa horizontal trim arrangement of an arc lamp employing a refractory ignitor for self-starting.

FIG. 10 is an enlarged view of the contact area between the negative electrode rod and the pointed end of the ignitor shown in FIG. lb.

FIG. 1d is an enlarged view of the contact area between the positive electrode rod and the bifurcated end of the ignitor shown in FIG. lb.

FIGS. 2a through 2g are isometric views of various ignitor shapes.

Referring to the drawing there is shown in FIG. la an angular trim arrangement of an arc lamp 1 comprising positively polarized electrode rod 2 and negatively polarized electrode rod 3, both suitably supported and spaced apart by conventional means not shown. The longitudinal axis of rod 3 is at an angle with reference to the longitudinal axis of rod 2 and their respective ends define a gap A which is adjustable for optimum arcing. Electrode rod 2 is initially provided with a recess 4 shown as a solid curved line while recess 5, shown as a broken curved line, represents the recess depth of a partially consumed electrode rod. Rod 3 is provided with a tapered portion 6 having a flat or slightly recessed tip section 7. ignitor 10 has a bifurcated configured V" slot 8 at one end which is made to engage annular lip projected member 11 of rod 2 while at its opposite end a conical projected member 9 is made to contact and seat upon tip section 7 of rod 3. It can readily be seen that the optimum gap length A can be maintained under all physical conditions of the rods 2 and 3 using the ignitor of this invention since the common contact area 12 .tbetween V slot 8 and lip 11 is variable. In addition, the increase in the crater depth from recess 4 to recess 5 has no apparent effect in positioning ignitor 10 within the optimum gap spacing A."

In the operational mode of the arc lamp, electrode rods 2 and 3 are initially spaced an optimum distance apart with rod 3 positioned with respect to rod 2 at an angle, measured clockwise from rod 2 to rod 3, between about and about 180", preferably between about and about depending on the particular lamp apparatus used. V" slot 8 of ignitor 10 is slipped onto lip 11 of rod 2 and then projection 9 is positioned to contact, and be secured in, tip section 7 of rod 3. Sometimes projection 9 is imbedded slightly into tip section 7 so as to form a good physical contact. Alternatively, projection 9 could be fabricated with a small bifurcated configuration which could more effectively engage the tip protrusion on section 7. With ignitor 10 secured in position, the positive and negative terminals of a power supply (not shown) are suitably coupled to rods 2 and 3, respectively, initiating a current flow through rods 2 and 3 and ignitor 10. Ignitor l0, acting as a short between rods 2 and 3, provides an ionized path therebetween which facilitates the ignition of an arc. Immediately upon arcing, ignitor 10 is dislodged from the gap and falls free.

FIGS. lb, 10 and 1d show a similar arc lamp as shown in FIG. 1a except that instead of an angular trim arrangement, a horizontal trim arrangement is shown. Arc lamp 32 comprises positively polarized electrode rod 22 and negatively polarized electrode rod 23. Rod 22 is initially fabricated with recess 24, shown as a solid curved line, while recess 25, shown as a broken curved line, represents the recess depth of a partially consumed electrode rod. Rod 23 is provided with a tapered portion 26 having a somewhat flat tip section 27. Ignitor 20 has a V slot 28 at one end which is fabricated to engage annular lip projection 21 of rod 22 while at its opposite end conical projected member 29, fabricated with a smaller V slot 30, engages tip section 27 of rod 23. Again it can be seen that the optimum gap length A can easily be maintained using thisignitor since the common contact area 31 between V" slot 28 and lip member 21 is variable. The operation of this are lamp arrangement is the same as that of FIG. la.

The geometrical configurations of several embodiments of the ignitor of this invention are shown in FIGS. 2a through 2g. Each of the ignitors 40 through 45 of FIGS. 2a through 2f, respectively, have two basic similarities, a pointed projection on one end and a bifurcated configured shape at the other end. The preferred embodiment of the invention, ignitor 46 shown in FIG. 2g, differs from ignitor 40, shown in FIG. 2a, in that it has a small bifurcated slot machined into its pointed projected segment so as to provide a more secure engagement with the negative rod. The exact body shape of the ignitor between the end projections is variable and can include any solid body having a circular or polygonially shaped cross-sectional area that remains constant or varies along the longitudinal axis of the ignitor. For example, FIGS. 20 through 2f show ignitors designed with cylindrical (40), rectangular (41), hexagonal (42), half rod (43), conical (44) and necked shaped (45) body configurations, respectively.

It will be appreciated that the foregoing examples of ignitors are merely illustrative and many more modifications in the body design of the ignitors are possible. In addition, when the pointed projected end of the ignitor is fabricated with a small bifurcated contour, the negatively polarized electrode rods may be designed with a corresponding lip projection similar to the lip projection of the positive rod shown in FIG. la except that it would be much smaller in size.

EXAMPLE I' In a similar configuration as shown in FIG. la, a positive carbon electrode l8 inches long by 0.535 inch in diameter was positioned at an angle of about 52 with respect to a negative copper coated carbon electrode measuring 9 inches long by contacted and-securely engaged the tapered end of the nega-- tive electrode rod as shown in FIG. 1c. The gap, with the ignitor assembled in place, measured 21/32 inch. A 47-volt, 135- ampere power supply was applied to the electrodes thereby initiating a current flow through the ignitor which ionized the dielectric air medium in the gap causing an arc to be struck and the ignitor to be ejected. The power supply was maintained relatively constant, for minutes, after which it was discontinued thereby terminating the arc. The ignitor was again assembled between the same electrodes and a gap of 21/32 inch was measured. The power was again applied as above and an arc was struck which again ejected the ignitor.

What is claimed is:

1. In an arc lamp comprising two electrodes with a gap therebetween, the improvement which comprises a refractory solid elongated ignitor having a bifurcated configured contour at one end and a pointed projection at the opposite end, said ignitor being positioned in said gap between said electrodes and contacting said electrodes so that upon the application of a power source to said electrodes the ignitor will act as a short therebetween to facilitate the striking of an arc across the gap which in turn will dislodge said ignitor.

2. The arc lamp of claim 1 wherein the elongated body between the bifurcated configured contour and the pointed projected end of said ignitor has a circular-shaped cross section.

3. The are lamp of claim 2 wherein the area of said circularshaped cross section varies along the longitudinal axis of the ignitor.

4. The arc lamp as in claim 1 wherein the elongated body between the bifurcated configured contour and the pointed projected end of said ignitor has a polygonially shaped cross section.

5. The are lamp as in claim 4 wherein the area of said polygonially shaped cross section varies along the longitudinal axis of the ignitor.

6. The are lamp of claim I wherein one of said electrodes has an annular projection lip at its end facing the gap and the other electrode has a tapered projection at its end facing the gap.

7. The are lamp of claim 6 wherein said bifurcated configured contour at one end of the ignitor is a V" slot.

8. The arc lamp of claim 7 wherein said pointed projected end of the ignitor has a bifurcated slot in its pointed end.

9. The arc lamp of claim 8 wherein said bifurcated slot in the pointed projected end ofthe ignitor is a V" slot.

10. The are lamp of claim 9 wherein said ignitor has a cylindrical elongated body. 11. The arc lamp of claim 1 wherein said ignitor is composed from at least one of the materials selected from the group consisting of carbon, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum and tungsten. I

12. The arc lamp of claim 11 wherein said ignitor contains at least one supporter material selected from a group consisting of the sulfur and silicon compounds of cesium, rubidium, potassium and calcium.

13. The are lamp of claim 10 wherein said ignitor is composed of carbon. 

1. In an arc lamp comprising two electrodes with a gap therebetween, the improvement which comprises a refractory solid elongated ignitor having a bifurcated configured contour at one end and a pointed projection at the opposite end, said ignitor being positioned in said gap between said electrodes and contacting said electrodes so that upoN the application of a power source to said electrodes the ignitor will act as a short therebetween to facilitate the striking of an arc across the gap which in turn will dislodge said ignitor.
 2. The arc lamp of claim 1 wherein the elongated body between the bifurcated configured contour and the pointed projected end of said ignitor has a circular-shaped cross section.
 3. The arc lamp of claim 2 wherein the area of said circular-shaped cross section varies along the longitudinal axis of the ignitor.
 4. The arc lamp as in claim 1 wherein the elongated body between the bifurcated configured contour and the pointed projected end of said ignitor has a polygonially shaped cross section.
 5. The arc lamp as in claim 4 wherein the area of said polygonially shaped cross section varies along the longitudinal axis of the ignitor.
 6. The arc lamp of claim 1 wherein one of said electrodes has an annular projection lip at its end facing the gap and the other electrode has a tapered projection at its end facing the gap.
 7. The arc lamp of claim 6 wherein said bifurcated configured contour at one end of the ignitor is a ''''V'''' slot.
 8. The arc lamp of claim 7 wherein said pointed projected end of the ignitor has a bifurcated slot in its pointed end.
 9. The arc lamp of claim 8 wherein said bifurcated slot in the pointed projected end of the ignitor is a ''''V'''' slot.
 10. The arc lamp of claim 9 wherein said ignitor has a cylindrical elongated body.
 11. The arc lamp of claim 1 wherein said ignitor is composed from at least one of the materials selected from the group consisting of carbon, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum and tungsten.
 12. The arc lamp of claim 11 wherein said ignitor contains at least one supporter material selected from a group consisting of the sulfur and silicon compounds of cesium, rubidium, potassium and calcium.
 13. The arc lamp of claim 10 wherein said ignitor is composed of carbon. 